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Fix #18246: correctly compute capture sets in TypeComparer.glb #18254

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Merged
merged 3 commits into from
Jul 23, 2023
Merged

Fix #18246: correctly compute capture sets in TypeComparer.glb #18254

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7f20c7f
Fix capture set handling in `distributeAnd`
Linyxus Jul 20, 2023
efe28db
Add test case for #18246
Linyxus Jul 20, 2023
4c807c5
Roll the `isAlwaysEmpty` optimisation into `capturing`
Linyxus Jul 23, 2023
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9 changes: 4 additions & 5 deletions compiler/src/dotty/tools/dotc/core/TypeComparer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -2610,12 +2610,11 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
case tp1: TypeVar if tp1.isInstantiated =>
tp1.underlying & tp2
case CapturingType(parent1, refs1) =>
if subCaptures(tp2.captureSet, refs1, frozen = true).isOK
val refs2 = tp2.captureSet
if subCaptures(refs2, refs1, frozen = true).isOK
&& tp1.isBoxedCapturing == tp2.isBoxedCapturing
then
parent1 & tp2
else
tp1.derivedCapturingType(parent1 & tp2, refs1)
then (parent1 & tp2).capturing(refs2)
else tp1.derivedCapturingType(parent1 & tp2, refs1)
case tp1: AnnotatedType if !tp1.isRefining =>
tp1.underlying & tp2
case _ =>
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/Types.scala
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Expand Up @@ -1940,7 +1940,7 @@ object Types {
* the two capture sets are combined.
*/
def capturing(cs: CaptureSet)(using Context): Type =
if cs.isConst && cs.subCaptures(captureSet, frozen = true).isOK then this
if cs.isAlwaysEmpty || cs.isConst && cs.subCaptures(captureSet, frozen = true).isOK then this
else this match
case CapturingType(parent, cs1) => parent.capturing(cs1 ++ cs)
case _ => CapturingType(this, cs)
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7 changes: 7 additions & 0 deletions tests/neg-custom-args/captures/cc-glb.check
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@@ -0,0 +1,7 @@
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/cc-glb.scala:7:19 ----------------------------------------
7 | val x2: Foo[T] = x1 // error
| ^^
| Found: (x1 : (Foo[T]^) & (Foo[Any]^{io}))
| Required: Foo[T]
|
| longer explanation available when compiling with `-explain`
8 changes: 8 additions & 0 deletions tests/neg-custom-args/captures/cc-glb.scala
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@@ -0,0 +1,8 @@
import language.experimental.captureChecking
trait Cap
trait Foo[+T]

def magic[T](io: Cap^, x: Foo[T]^{io}): Foo[T]^{} =
val x1: Foo[T]^{cap} & Foo[Any]^{io} = x
val x2: Foo[T] = x1 // error
x2 // boom, an impure value becomes pure